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// initialization/TankTest.java

// TIJ4 Chapter Initialization, Exercise 12, page 177

/* Create a class called Tank that can be filled and emptied, and has a

* termination condition that it must be empty when the object is cleaned up.

* Write a finalize() that verifies this termination condition. In main(), test

* the possible scenarios that can occur whtn your Tank is used.

*/

class Tank {

int howFull = 0;

Tank() { this(0); }

Tank(int fullness) {

howFull = fullness;

}

void sayHowFull() {

if(howFull == 0) System.out.println("Tank is empty");

else System.out.println("Tank filling status = " + howFull);

}

void empty() {

howFull = 0;

}

protected void finalize() {

if(howFull != 0)

System.out.println("Error: Tank not empty");

// Normally, you'll also do this:

// super.finalize(); // Call the base-class version

}

}

public class TankTest {

public static void main(String[] args) {

Tank tank1 = new Tank();

Tank tank2 = new Tank(3);

Tank tank3 = new Tank(5);

// Proper cleanup: empty tank before going home

tank2.empty();

// Drop the reference, forget to cleanup:

new Tank(6);

System.out.println("Check tanks:");

System.out.println("tank1: ");

tank1.sayHowFull();

System.out.println("tank2: ");

tank2.sayHowFull();

System.out.println("tank3: ");

tank3.sayHowFull();

System.out.println("first forced gc():");

System.gc();

// Force finalization on exit but using method

// deprecated since JDK 1.1:

System.out.println("try deprecated runFinalizersOnExit(true):");

System.runFinalizersOnExit(true);

System.out.println("last forced gc():");

System.gc();

}

}